Melting Antarctic glacier in state of 'irreversible retreat' experts say

This 19-mile crack appeared in the massive Pine Island Glacier in October 2011and led to the "calving" of an iceberg the size of Chicago. (Source: NASA/GSFC/METI/ERSDAC/JAROS, and U.S. Japan ASTER Science Team.)

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A colossal Antarctic glacier has been rapidly receding and now scientists say it has likely reached a point of uncontrollable retreat. Continued melting of the glacier and the surrounding ice sheet could trigger a dangerous rise in Earth's sea level.

Researchers at the French National Center for Scientific Research in Grenoble have built an ice-flow modelindicating that the Pine Island Glacier, which makes up about 10 percent of the total ice on the West Antarctic Ice Sheet, will continue to recede.

"[The Pine Island Glacier] has started a phase of self-sustained retreat and will irreversibly continue its decline," said Gael Durand, a glaciologist from France.

The melt from the Pine Island Glacier, which is located on the West Antarctic Ice Sheet, contributes about 20 percent of the total ice loss from Antarctica, according to a report by the British Antarctic survey. It is the single largest contributor to sea-level rise in Antarctica.

An international team of scientists in January reported in the journal Nature Climate Change that recent, rapid thinning of the glacier had likely reached a tipping point and will continue unabated.

The French study noted that the grounding line – the place where the part of the glacier that is on land meets its ice shelf, which extends over the water – is on the verge of retreating over an oceanic trench that would allow more water to seep underneath the glacier and accelerate melting, according to an article in livescience.com.

The means the glacier is more prone to collapse, triggering a rapid melting of the Antarctic Ice Sheet.

Scientists' ice-flow models estimate that over the next 20 years the slowly dying glacier will shed as much as 100 billion tons of water, causing global sea levels to rise 3.5 to 10 mm, or 0.14 inches to 0.39 inches.

That doesn't sound like much, but greater rises in sea level are possible because the glacier's instability can have a domino effect on the remainder of the West Antarctic Ice Sheet, said Dr. G. Hilmar Gudmundsson of the British Antarctic Survey, who was involved in the project.

"At the Pine Island Glacier, we have seen that not only is more ice flowing from the glacier into the ocean, but it's also flowing faster... We also can see this boundary is migrating further inland," Gudmundsson said in a statement.

One model suggests that the Pine Island Glacier is set to lose as much as 50 percent of its ice in the next 100 years, and in that time the grounding line will have retreated by more than 200 kilometers (124.3 miles).

The United Nations' climate science body, the Intergovernmental Panel on Climate Change (IPCC) has projected that sea levels are likely to rise between 10.4 and 32.8 inches by 2100.

Some researchers believe the demise of the Pine Island Glacier could have the same effect on surrounding glaciers, leading to a collapse of the entire ice sheet, raising global sea level by 10 to 16 feet.

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